1. Technical Field
The present invention relates to an electrophoretic display device and an electronic apparatus including the electrophoretic display device.
2. Related Art
In known electrophoretic display devices (EPD), an electrophoretic dispersion liquid which is prepared by dispersing particles by a dispersion medium is sealed between a pair of substrates. An example of related art, JP-A-2010-91908, discloses an electrophoretic display device in which white particles (for convenience, hereinafter referred to as “white particles”) and black electrophoretic particles (for convenience, hereinafter referred to as “black particles”), each having been electrically charged to opposite polarities, are dispersed into a dispersion medium and a voltage is applied between a pixel electrode formed on one substrate and an opposite electrode formed on the other substrate.
According to an electrophoretic display device, a voltage is applied between the pixel electrode and the opposite electrode thereby moving the white particles and the black particles toward different substrates opposite to each other respectively, so that an image can be displayed on a display surface.
Further, other examples of related art, JP-A-2003-5226 and JP-A-2003-5225, respectively disclose an electrophoretic display device in which black particles are dispersed into a dispersion medium, and the display includes a first display electrode located along the lower face of a stepped portion formed on one substrate for each pixel, and a second display electrode located along the upper face of the stepped portion, wherein the area that the first display electrode is formed in is colored in black and the area that the second display electrode is formed in is colored in white.
According to such an electrophoretic display device, it is possible to render a display in black or white for each pixel by applying a voltage between the first display electrode and the second display electrode so as to move the black particles to cover the first display electrode or the second display electrode. Further, this electrophoretic display device includes partition members disposed to surround the periphery of each pixel in order to inhibit the electrophoretic particles from moving between different pixels.
According to the electrophoretic display device disclosed in JP-A-2010-91908, when white color is to be displayed on a display surface, for example, the smaller the thickness of a white particle layer including a plurality of white particles is, the harder it becomes to sufficiently cover up the black particles moved to the opposed electrode side with the white particle layer, thus threatening a reduction in the reflection ratio of the white color. Therefore, in order to secure high-quality display, when displaying white on the display surface, the thickness of the white particle layer needs to be thick enough to be able to sufficiently cover up the black particles which were moved toward the pixel electrodes. This has posed a technical problem where the distance between opposite electrodes and pixel electrodes (in other words, the distance between a pair of substrates) is difficult to shorten, which necessitates the voltage to be applied between the opposite electrodes and the pixel electrodes be relatively high in order to move the white particles and black particles.
Further, there has been posed another technical problem that if the number of white particles is increased to enlarge the thickness of the white particle layer used when displaying white on a display surface, the particle concentration in a dispersion liquid is increased, which threatens to slow down the movement of the electrophoretic particles, when a voltage is applied.
Furthermore, according to the electrophoretic display device of the above-referenced related arts, JP-A-2003-5226 and JP-A-2003-5225, a voltage is applied between the first electrodes located along the lower surface of the bottom of a recess of the stepped portion and the second electrode located along the upper surface of the stepped portion, which causes the direction of an electric field to differ from the direction of electrophoresis of the particles, that is, the electric field is directed to pass through the inside of the stepped portion. Consequently, the electrophoretic particle movement speed becomes slow, which means there is a concern that the speed of display switching may become slow. In addition, partition wall members are disposed to surround the periphery of each pixel, causing an effective display region capable of displaying effectively to be smaller by the same amount of region area occupied by the partition walls, which makes it difficult to achieve high-quality display performance. Thus, there is still another technical problem.